Sample revocation

Mask editor interface.
At very high Aggressiveness settings to deal with extremely challenging data, you can use sample revocation to tell Wipe where it should NOT look for background. This may help protect areas of detail you are certain are real, and should achieve superior results.

With the exception of the previously mentioned larger "dark anomalies" (such as dust donuts or clumps of dead pixels), it is typically unnecessary to provide Wipe with a mask. However if you wish to give Wipe specific guidance as to which areas of the image to include in the model of the background, then you may do so with a mask that describes which where background definitely does not exist.

This is a subtle but important distinction from background extraction routines in less sophisticated software, where the user must "guess" where background definitely exists. The former is easy to determine and is readily visible, whereas the latter is usually impossible to see, precisely because the background is mired in gradients. In other words, StarTools' Wipe module works by sample revocation ("definitely nothing to see here"), rather than by the less optimal (and possibly destructive!) sample setting ("there is background here").

Analogous to how sample setting routines yield poor results by accidentally including areas of faint nebulosity, the opposite is the case in Wipe; accidentally masking out real background will yield the poorer results in Wipe. Therefore, try to be conservative with what is being masked out. If in doubt, leave an area masked in for Wipe to analyse.